Recently, cars, home electric appliances, cameras, containers, etc. are required to be lighter in weight. As such, various elements of machines, appliances, etc have been changed from metal to plastic.
Parts made of plastic consist of a plurality of molded bodies (described as first a molded body or bodies in the following description), and sealing parts (described as a second molded body or bodies in the following description). Sealing parts are made of such elastic polymers as silicon gum, urethane gum, styrene-butadiene gum, etc., and are used in assembling sections between parts made of plastics so as to provide sealing, absorbing or nonskid capabilities for products manufactured therewith.
Conventionally, the second molded bodies are independently molded from the first molded bodies, and then they are manually assembled into the first molded bodies. In such a method, there are disadvantages of lower assembly precision and increasing assemblying steps. To solve these disadvantages, there was disclosed a method of multi-injection molding in Japanese Provisional Publication (Kokai) Gazette No. 60-52322 and Japanese Provisional Publication (Kokai) Gazette No. 63-104809 This method comprises the steps of molding a first molded body having an aperture on the surface thereof by injection molding, and injecting an elastic polymer for forming a second molded body in the slot or channel. In this conventional method, multi-injection molded bodies consisting of the first molded body and the second molded body are molded in one injection molding step, so that assembling precision can be increased, and assembling steps can be reduced.
In the above conventional method, first molded bodies are molded by injection molding, and the walls of the apertures are formed approximately vertical from the bottom faces thereof, in order that one can easily remove products from the molding machines. But in the above method, the second molded bodies, molded in the apertures of the first molded bodies, can also be easily pulled out of the first molded bodies because no way is provided for engaging on the side wall faces of the apertures. In order to fix second molded bodies in the channels of the first molded bodies, as disclosed in the gazett No. 63-104809, reactive elastomer layers, primer layers, etc. are formed between the inner bottom faces of the apertures of the first molded bodies and the botton faces of the second molded bodies, causing them to adhere together.